What Is a Particle Accelerator?

A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in particle physics as colliders (e.g. the LHC at CERN, KEKB at KEK in Japan, RHIC at Brookhaven National Laboratory, and Tevatron at Fermilab), or as synchrotron light sources for the study of condensed matter physics.

Smaller particle accelerators are used in a wide variety of applications, including particle therapy for oncological purposes, radioisotope production for medical diagnostics, ion implanters for manufacture of semiconductors, and accelerator mass spectrometers for measurements of rare isotopes such as radiocarbon. There are currently more than 30,000 accelerators in operation around the world.

There are two basic classes of accelerators: electrostatic and electrodynamic (or electromagnetic) accelerators. Electrostatic accelerators use static electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator.

A small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, which is limited by electrical breakdown.

Electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields (either magnetic induction or oscillating radio frequency fields) to accelerate particles.

Since in these types the particles can pass through the same accelerating field multiple times, the output energy is not limited by the strength of the accelerating field. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators.

Rolf Widerøe, Gustav Ising, Leó Szilárd, Max Steenbeck, and Ernest Lawrence are considered pioneers of this field, conceiving and building the first operational linear particle accelerator, the betatron, and the cyclotron.

Because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators (but not ion facilities) actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general.

Scientists first learned about subatomic particles, such as protons, neutrons, and electrons, in the early 20th century. Particle accelerators were invented in the 1930s to allow scientists to learn even more about the internal structure of the atom.

Over the years, particle accelerators have revealed that the internal structure of the atom is more complex than scientists had imagined. In addition to learning more about the fundamental physics of matter, scientists also believe particle accelerators can help us understand the forces that existed at the very creation of the universe.

Experts estimate there are over 30,000 particle accelerators in use around the world. There are two basic types of particle accelerators: linear and circular. In a linear accelerator, particles travel in a straight line from one end to the other. In a circular accelerator, particles travel repeatedly around a loop.

Particle accelerators use different types of technology to work their magic. For example, electric fields are used to accelerate particles as they travel through a vacuum inside a metal pipe. To create calculated collisions, large electromagnets precisely direct the particles to their targets, which could be thin pieces of metal or another beam of particles.

After the collision takes place, sophisticated particle detectors are used to detect and record the radiation and particles produced. Scientists examine the results to gain a better understanding of particle physics. Beyond the world of physics, the results of particle acceleration experiments have been used for many other purposes, including medical research, development of new technologies and products, and even national security.

When it comes to particle accelerators, there’s one that stands head and shoulders above the rest: the Large Hadron Collider (LHC). Located at CERN in Geneva, Switzerland, the LHC consists of approximately 17 miles of tunnels that sit nearly 600 feet below the border of Switzerland and France.

The LHC accelerates two beams of protons in opposite directions around the tunnels. The beams of protons are steered by a system of electromagnets about 100,000 times stronger than Earth’s magnetic field. To counteract the heat produced in the process, the world’s largest cryogenic system keeps the electromagnets cooled to a temperature of -456º F!

The LHC gets all those protons it uses, from a single bottle of hydrogen gas that only needs to be replaced twice each year. Scientists have used the LHC to try to recreate the conditions immediately following the Big Bang at the beginning of the universe. In 2012, scientists using the LHC discovered the Higgs boson, the subatomic particle believed to hold the key to understanding how particles get their mass.

Content for this question contributed by Philip Trach, resident of Easton, Northampton County, Pennsylvania, USA